Paper is being widely used as, for example, various packaging paper, carrier bags, and folding paper for its excellent fold holding property. Paper, however, is inferior in water resistance, so that paper sometimes causes breakage or discoloration of printing when being wet by, for example, rain. Further, paper has no transparency to have a problem of not allowing contents to be seen therethrough when served for packaging as, for example, a bag. Therefore, a plastic film has been studied as a product in place of paper.
Transparent cellophane has been used as a film excellent in fold holding property. Cellophane, however, has hygroscopicity to vary its characteristics depending on the season, making it difficult to supply cellophane with constant product quality, and cellophane has been recognized to have a drawback for its bad processability attributed to ununiformity of thickness.
On the other hand, a polyethylene terephthalate film has an advantage of having excellent characteristics such as toughness, water resistance, and transparency, whereas it has had a drawback of being inferior in fold holding property.
As a method of overcoming this drawback, a polyethylene terephthalate film has been disclosed that is reduced in density of the film to be capable of retaining a good fold holding property (for example, see Patent Document 1).
The polyethylene terephthalate film in Patent Document 1, however, has a problem of having a large heat shrinkage property. It is pointed out that leaving a bag or the like including such a film in, for example, a car in midsummer or a warehouse without a temperature controller makes the bag or the like unusable due to shrinkage or distortion of the film. Further, such a film also has had a problem of being unprocessable for its shrinkage in a working process, such as printing on the film, that requires high temperature.
When a film excellent in fold holding property is processed into a bag shape for use, the film can be closed at its opening only by twisting to give a merit of requiring no work such as tying the opening. A polyethylene film is known as a film excellent in fold holding property (for example, see Patent Document 2). The polyethylene film in Patent Document 2, however, has a drawback of being insufficient in aroma retaining property. When contents in a bag have smell, the smell passes through the polyethylene film even with the opening of the bag closed.